Process and apparatus for forming battery plates

ABSTRACT

A process for cutting a moving strip to form a series of plates, such as battery plates, includes the initial step of transporting the strip past a rotary divider including a cutter having radial blades configured to cut the strip into the plates. The cutter further has a set of blades for cutting individual pieces from the strip, which pieces are not part of the plates. As the cutter blades cut the strip to form the plates and pieces, a vacuum system applies suction to draw the pieces cut from the strip inwardly into the cutter through holes in the cutter, and then out of the cutter. The holes are each located adjacent each one of the corresponding blades and are shaped and positioned to permit the cut-away piece to pass through. In a preferred embodiment, the vacuum system includes a pair of vacuum manifolds that apply suction at opposite ends of the cylindrical cutter. An apparatus for carrying out the foregoing process accordingly includes a rotary divider as described above provided with a vacuum system. Battery plates made according to the foregoing process are improved in that the two lower corners have a rounded shape lacking a sharp edge which tends to tear an adjacent separator. Such a plate may be inserted bottom end first into a separator envelope to form a plate element for use in a lead-acid battery.

This application is a divisional of U.S. patent application Ser. No.07/909,247, filed 06 Jul. 1992, now U.S. Pat. No. 5,384,217.

TECHNICAL FIELD

The present invention relates to the manufacture of plates from a movingstrip by cutting the strip, particularly to the manufacture of batteryplates for use in lead-acid batteries.

BACKGROUND OF THE INVENTION

A plate for a lead-acid battery is conventionally made by applying abattery paste to a conductive support such as a lead alloy grid. Thepaste is made from lead oxide, sulfuric acid and water. The lead oxidereacts with the sulfuric acid to form mono-, tri- or tetrabasic leadsulfate(s). Dry additives such as fiber and expander may be added. Themixture is then dried and water is re-added to form a paste of thedesired consistency. The paste is applied to the lead grid, and thepasted plates are then flash-dried and cured at an elevated temperatureand humidity to oxidize free lead and adjust the crystal structure ofthe plate. After curing, the positive plates are assembled intobatteries and electrochemically formed by passage of current to convertthe lead sulfate or basic lead sulfate(s) to lead dioxide, therebyforming the active lead material.

The lead alloy grid is made in a multistage process in which molten leadalloy is cast to form a strip. The strip is expanded to form meshelements for grids, and the paste is then applied. Liner papers areapplied to the surfaces of freshly pasted plates during the pastingoperation to facilitate handling and stacking. Individual plates areformed by passing the pasted strip through a rotary divider that cutsthe outlines of the individual plates on the moving strip. To ensureproper registration for cutting, the strip is formed during expansionwith a series of regularly spaced central recesses that are engaged bylugs of a drive roller associated with the divider. The cut plates arethen flattened, flash-dried, and stacked for later use in lead-acidbattery manufacture.

The battery grids each take the form of a generally rectangular framesupporting a mesh of grid elements onto which the paste is applied. Theframe has a pair of upper corners and a pair of lower corners, and anelectrically conductive tab extending from a location between the twoupper corners. In one common battery design, every other plate in thebattery stack is inserted into an envelope made of a separator materialsuch as submicro polyethylene. The sides of the envelope act asseparators between the plate in the envelope and the two adjoiningplates in the battery stack.

In assembling a battery of this kind, it is necessary to insert thebattery plate bottom-first into the open end of the envelope so that theconductive tab at the top of the plate extends out of the envelope.However, the bottom corners on the battery plates are sharp, and willsnag and tear the separator material between the positive and negativeplates, causing an electrical short within the battery and reducingbattery life. Bending or vibration of the plate disposed in the envelopeduring assembly or use can also cause tearing, and the problem is notconfined to envelope-style separators.

Use of battery plates with rounded bottom corners would eliminate thesnag and tearing of separators, but no practical process has beenproposed for producing rounded corners on such battery plates. Inparticular, any process wherein the rotary divider cuts off cornersresults in small pieces of trim (scrap) that are severed from the strip.These pieces, if left on the strip after cutting, can come loose andcause cutting die failure on the divider and can lead to battery failureif the pieces are carried over and inadvertently incorporated into thefinished battery. The present invention addresses these problems byproviding a system for cutting the rounded corners and then removing thepieces during continuous plate manufacture.

SUMMARY OF THE INVENTION

A process for cutting a moving strip to form a series of plates, such asbattery plates, initially involves transporting the strip past a dividerhaving a rotary cutter with a first set of blades extending radiallytherefrom configured to cut the strip into the plates, and a second setof radial blades for cutting individual pieces from the strip. As theblades cut the strip to form the plates and pieces, a vacuum systemapplies suction to draw the pieces cut from the strip inwardly into thecutter through holes in the cutter, and then out of the cutter. Theholes are each located adjacent one of the corresponding cutter bladesof the second set and are shaped and positioned to permit the cut-awaypiece to pass through. In a preferred embodiment, the vacuum systemincludes a pair of vacuum manifolds that apply suction at opposite endsof the cylindrical cutter.

An apparatus for carrying out the foregoing process accordingly includesa rotary divider having a cylindrical cutter configured to cut the stripinto the plates, including a second set of blades for cutting individualpieces from the strip as described above, and a vacuum system thatapplies suction to draw the pieces cut from the strip inwardly into thecutter through the holes in the cutter, and then out of the cutter.

According to a further aspect of the invention, a conventional batteryplate as described above is improved in that the two lower corners havea rounded shape lacking a sharp edge which would tend to tear anadjacent separator. Such a plate may be inserted bottom end first into aseparator envelope to form a plate element for use in a lead-acidbattery.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numerals denote like elements, and:

FIG. 1 is a schematic diagram of an overall process for making batteryplates in which the process of the invention is included, with the shapeof the strip at each stage shown below;

FIG. 2 is a schematic diagram of a vacuum system used with a divideraccording to the invention;

FIG. 3 is a schematic side view of the divider and flattener apparatusused in the process of FIG. 1;

FIG. 4 is a perspective view of a divider apparatus according to theinvention;

FIG. 5 is a partial perspective view of the cylindrical cutter shown inFIG. 4;

FIG. 6 is partial front view, partly in section, of the left end of thedivider shown in FIG. 4; and

FIG. 7 is a front view of a battery plate element according to theinvention, with the concealed portion of the plate shown in phantom.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, the process according to the invention is shown inrelation to the other steps conventionally used in a continuous processfor making lead-acid battery plates. The known process for making suchplates includes an initial step 21 of melting hog lead in a furnace,followed by a step 22 of feeding molten lead alloy to a strip caster.Trim from the caster is recycled to the furnace. The strip is coiled(23) on a winder, and coils of lead alloy strip are stored for lateruse.

To form a battery grid, the coil is unwound (24) and the free end is fedthrough an expander that cuts, slits and stretches (25) the strip toform a mesh-like pattern of grid elements. See, for example, theexpanders described in U.S. Pat. Nos. 4,315,356 and 4,291,443 assignedto Cominco Ltd., the contents of which are incorporated herein byreference. Trim from the expander is recycled to the furnace. Theexpanded strip is then pasted (26) by a conventional paster, and thenfed to the divider according to the invention, wherein the strip is cut(27). Plates cut from the strip are then flattened (28), then passed ona conveyer through an oven for flash-drying (29), and then stacked (30)for later use. Flash drying is performed using an open gas flame or anoven, for example, as a 10-15 second drying of the plates in aconventional blast drying oven at 260° C. (500° F.).

A shown in FIG. 2, a rotary divider 31 used in the cutting step has avacuum system 32 associated therewith. Divider 31 cuts the moving stripinto plates and, at the same time, cuts rounded corners as explained indetail below. Each pair of corners cut results in a small, roughlytriangular piece of trim (scrap metal.) Vacuum system 32 includes acyclone blower 33 connected to a cyclone 34 by a conduit 35. Cyclone 34is in turn connected to a pair of manifolds 36 disposed at opposite endsof divider 31 through a pair of hoses or pipes 37. The trimmed piecesfrom divider 31 enter manifolds 37 and pass through hoses 37 intocyclone 34. The pieces then fall out of the bottom of cyclone 34 into abarrel 38. The contents of barrel 38 may be periodically recycled to asmelter.

Referring now to FIGS. 3 and 4, the divider 31 is located immediatelyahead of a flattener 39. A pasted strip 41 has a series of regularlyspaced holes 42 which are engaged by lugs or dogs 43 of an optionalfirst drive roller 44. Roller 44 may comprise a series of spaced,coaxial disks of equal diameter that receive strip 41 from the paster,with lugs 43 being on the center disk. Strip 41 then moves over severalspaced, parallel support rails 46 into a nip 47 between a second driveroller 48 and a cylindrical cutter 49.

Cutter 49 simultaneously cuts strip 41 into two rows of battery plates41A having rounded outside (bottom) corners 51. A freely-rotatablerotary brush 52, for example, a 2-inch diameter nylon brush, contactsthe cylindrical outer surface of cutter 49 tangentially, preferably fromend to end, cleaning it and aiding in forcing the trim pieces into theinterior of cutter 49. All of rolls 44, 48 and 49 are driven by asuitable drive system 53 such as an electric motor provided with a gearlinkage (not shown) that ensures that rolls 44, 48 and 49 rotatetogether at the same speed.

Flattener 39 includes pair of upper and lower conveyer belts 56, 57wound over a series of spaced pairs of upper and lower rollers 58, 59and spaced apart by a distance approximately equal to the platethickness, e.g., 0.04 inch. The plates 41A are fed between belts 56, 57.The action of rollers 58, 59 flattens out any raised edges which mayhave formed during cutting. Rollers 58, 59 have an associated drivesystem but need not be biased to exert extra pressure on plates 41A.

FIGS. 4 to 6 illustrate the divider 31 in detail. Rotary cutter 49,which is preferably a cylindrical drum, has a plurality of cutter blades61 projecting radially from its cylindrical surface in a repetitivepattern that forms two offset rows of plates 41A. Blades 61 includelengthwise blades 61A that form the sides of each plate 41A, centraltransverse blades 61B for forming the tab on each plate, and roundedblades 61C for forming the rounded lower corners of each plate. Blades61B alternate with a row of central recesses 62 that mate with lugs 43of drive roller 48, and blades 61B alternately face in oppositedirections to produce two rows of plates 41A from a single strip asshown. Blades 61A extend from one end of a blade 61B alternately inoffset positions towards each end of the roll, at which point each bladesplits into a pair of curved, symmetrical blades 61C. Each pair ofblades 61C cuts off a roughly triangular piece from strip 41 to form apair of rounded corners 51.

Rotary cutter 49 has a pair of axles 63 projecting from its endsrotatably supported by a pair of bearings 64; drive roller 48 issimilarly supported. Cutter 49 further has a pair of annular recesses 65in each end. Each recess 65 communicates with a series of spaced radialholes 66 each formed adjacent to and outwardly of an associated pair ofcutter blades 61C. Holes 66 match the size of the pieces trimmed by theblades 61C.

The vacuum manifolds 36 are mounted in contact with the rotating ends ofcutter 49 covering each recess 65. Each manifold comprises a pair ofmating sections 36A, 36B which are secured together by any appropriatemeans, such as screws or other fasteners, on opposite sides of each axle63. Sections 36A, 36B have semi-circular cutaway portions which form amanifold chamber 65A in communication with recess 65. An outlet opening65B in one section 36B allows cut-away corner pieces 67 to pass througha manifold extension 70 having a gradually reduced width, and then intohose 37, which is coupled to extension 70. For purposes of removingcorner pieces 67 from lead-acid SLI battery plates of conventional size,a minimum vacuum of about 9 inches of water is needed. If the processline is operating at a speed higher than about 100-130 feet/minute, astronger vacuum may be needed.

In operation, cutter 49 rotates to continuously cut plates 41A asdescribed above. Triangular trim pieces 67 are cut away from strip 41 byrounded blades 61C. These pieces 67 are drawn inwardly through holes 66by the suction applied by vacuum system 32 through manifolds 36. If thesuction is not sufficient to make each piece 67 fall in, brush 52contacts pieces 67 and presses them inwardly in combination with theforce of the suction. Pieces 67 enter annular recess 65 and theassociated manifold 36, after which they travel to barrel 38 viamanifold chamber 65A, outlet 65B, manifold extension 70, hose 37 andcyclone 34, as described above.

FIG. 7 illustrates a plate element 71 according to the inventionincluding a pasted plate 41A having rounded bottom corners 51, squaretop corners 72, and a conductive tab 73 extending from between the topcorners 72. The grid itself includes a generally rectangular outer frame74 and a mesh of grid elements spanning frame 74 which are covered bythe battery paste. Many different grid designs are well-known in theart. Each plate 41A is disposed in a conventional submicro polyethyleneseparator envelope 76. Envelope 76 is formed from a single piece ofmaterial which is folded in half and secured at the edges, for example,with crimped edges 77. During insertion or re-insertion of plate 41Ainto envelope 76, such as during the strap forming operation, roundedcorners 51 prevent tearing of envelope 76.

It will be understood that the foregoing description is of preferredexemplary embodiments of the invention, and that the invention is notlimited to the specific forms shown. For example, the process andapparatus according to the invention could be used to manufacturevirtually any type of plate, and are not limited to the manufacture ofbattery plates. The holes, blades and recesses of the cutter could berearranged to cut away small pieces at locations other than the bottomcorners as disclosed. These and other modifications may be made in thedesign and arrangement of the elements without departing from the scopeof the invention as expressed in the appended claims.

We claim:
 1. An apparatus for cutting a moving strip to form a series ofplates, comprising:a rotary divider including a cylindrical cutterhaving a first set of blades extending radially therefrom configured tocut the strip into the plates, and a second set of radial blades forcutting individual pieces from the strip, which pieces are not part ofthe plates; and a vacuum system that applies suction to draw the piecescut from the strip inwardly into the cutter through holes in the cutter,and then out of the cutter, wherein the first and second sets of bladesform a repetitive pattern on the cutter, and the divider furthercomprises a drive roll disposed adjacent and in parallel to thecylindrical cutter, which drive roll has a series of spaced radial lugsthat engage spaced recesses in the strip and corresponding spacedrecesses in the cutter when the strip comes into tangential contacttherewith to feed the strip into a nip between the drive roll and thecylindrical cutter.
 2. The apparatus of claim 1, wherein the second setof blades comprise regularly spaced pairs of rounded blades for cuttingrounded corner pieces from each plate, which rounded blades are disposedin two series near opposite ends of the cutter, the holes being adjacenteach rounded blade, and the cutter has a pair of recesses that open atopposite ends of the cutter in communication with the holes into whichrecesses the pieces are drawn by the vacuum system.
 3. The apparatus ofclaim 2, wherein the vacuum system comprises a source of suction and apair of vacuum manifolds connected thereto, which manifolds cover therecesses at opposite ends of the cutter so that suction applied at bothends of the cutter draws the cut pieces through the holes into therecesses and then into the vacuum manifolds.
 4. The apparatus of claim3, wherein the vacuum system further comprises a cyclone interposedbetween the vacuum manifolds and the source of suction, a pair of hoseswhich conduct the cut pieces to the cyclone from each manifold, and areceptacle for collecting the cut pieces from the cyclone.